(a) Field of the Invention
The present invention relates to a method of producing a flame-retardant acrylic polymer, and more particularly to a method of producing an acrylic polymer which can provide acrylic fibers, etc. having excellent flame retardancy, without impairing the intrinsic properties of the acrylic polymer. The method comprises polymerizing acrylonitrile (hereinafter referred to as AN) in a halogen-containing polymer aqueous latex.
(b) Description of the Prior Art
Acrylic fibers have a wool-like bulky touch, excellent physical properties, excellent dyed color fastness and dyed color clearness, and therefore they are used in wide fields of applications. However, since acrylic fibers are flammable like other natural and synthetic fibers, it is strongly demanded to give acrylic fibers flame retardancy in special uses, for example, interior furnishing such as carpets, curtains, etc. and clothing for babies and children.
Therefore, in recent years, there have been attempted various methods to make acrylic fibers flame-retardant, and the following methods have been proposed, for example: a method of post-treatment with a flame retardant; a method of copolymerizing a flame retardant monomer with AN; a method of blend-spinning a flame-retardant polymer with an AN (co)polymer, etc.
However, in the case of the post-treatment method, there are problems in washing fastness, touch of the fibers, etc.
In the case of the copolymerization method, although the flame retardancy can be improved by increasing the copolymerization ratio of the flame-retardant monomer, the limit of the flame-retardant monomer is at most from 20 to 25 weight %, so as to dissolve the copolymer in an inorganic solvent. When using an organic solvent, the copolymerization ratio can be increased to about 45 weight % to improve flame retardancy, but undesirable problems are then caused such as delustering, coloring, dyed color unclearness, lack of bending elasticity.
In the case of blend-spinning, for example when a vinyl chloride latex is blended with an acrylic spinning solution, especially in a spinning solution using an inorganic solvent, the latex agglomerates, and in the spinning step, spinnerette clogging and filament breakage upon stretching are frequently caused. Accordingly as in Japanese Patent Publication No. 42884/1977 filed by the Assignee, methods have been proposed to overcome this problem, by using a latex produced in the presence of a specific water-soluble polymer. Although some improvement can be attained by such methods, there is naturally a limit of the quantity of latex to be mixed. Therefore, even by such a method, it is still difficult to produce highly flame-retardant fibers, and because of poor compatibility of AN (co)polymer with vinyl chloride polymer, such a method still involves problems to be solved in practical properties such as transparency, gloss, dyed color clearness, etc.